In a conventional current sensing device disclosed in, for instance, JP 5-72233A, as shown in FIGS. 10A and 10B, a ring-shaped magnetic core 100 has a gap 100a and is provided to surround a conductive wire 105. When an electric current If flows in the conductive wire 105, a magnetic flux φ flows in the magnetic core 100 and a magnetic field H is formed in the gap 100a. The magnitude of the magnetic field H varies with the magnitude of the current If. A sensor package 110 including a sensor chip 111 such as a magnetism-responsive Hall element, which is mounted on a lead frame 113 and embedded in a resin mold 112, is disposed in the gap 100a. The sensor chip 111 produces an output signal having a magnitude corresponding to the magnitude of the magnetic field H. For easy installation, the center of the sensor package 110, specifically the lead frame 113 of the sensor package 110, is positioned on the center of the gap 100a of the magnetic core 100, that is, at the same distance D from the ends of the magnetic core 100 facing each other and defining the gap 100a. As a result, the sensor chip 111, particularly the Hall element (shown by dotted line), is offset from the center of the gap 100a. The sensor chip 111 is susceptible to external magnetic field other than the magnetic field generated by the current If, and the output signal includes errors.